Small-cell lung cancer (SCLC) is an aggressive malignancy with a poor prognosis. Despite the initial chemosensitivity, survival for extensive-disease (ED) SCLC remains limited. Immune checkpoint inhibitors (ICIs) in combination with chemotherapy have recently been redefined as the standard of care. We evaluated the efficacy of ICI combination therapy in clinical trials translated into real-world clinical practice for patients with ED-SCLC.

This retrospective cohort study analyzed data from the Tokushukai REAl World Data Project. Patients with ED-SCLC who received first-line platinum-based chemotherapy between April 2010 and March 2022 were included in this study. Overall survival (OS) was estimated using the Kaplan–Meier method, and associations with clinical variables were analyzed using Cox proportional hazards regression.

Among 590 patients (median age, 71 years; range, 40–90 years), 197 (33.4%) were aged ≥ 75 years. Following ICI approval in Japan in August 2019, 206 patients received first-line treatment, of whom 96 received ICI combination therapy. ICI-treated patients had significantly improved OS compared to chemotherapy alone (median 13.0 vs. 9.7 months; p = 0.011), with a pronounced benefit in those aged < 75 years (15.0 vs. 10.0 months; p = 0.022) but not in those aged ≥ 75 years (8.9 vs. 8.6 months; p = 0.647). The inverse probability of treatment weighting (IPTW) method resulted in an HR of 0.666 (95% confidence interval [CI] 0.483–0.919) in the overall cohort of patients. ICI combination therapy was an independent factor for improved OS (HR, 0.589; 95% CI, 0.447–0.776).

ICI combination therapy improved survival in real-world patients with ED-SCLC, aligning with the results of pivotal clinical trials. However, their limited efficacy in older adults underscores the need for tailored treatment strategies.